Booster-assisted fluid pressure compounding systems



June 15,1943. I s. SCHNELL 2,322,063

BQOSTER-ASSISTED FLUID PRESSURECOMPOUNDING SYSTEMS Filed March 28, 19422 Sheets-Sheet 1 3| C H63 70 ,63/ 62 60 v 7| 13 INVENTOR STEVESCHNELLATTORNEY 2 Sheets-Shae 2 S. SCHNELL BOOSTER-ASSISTED FLUID PRESSURECOMPOUNDING SYSTEMS June 15, 1943.

. INVENTOR s E ESCHNELL k BY ' ATTORNEY Patented June 15, 1943BOOSTER-ASSISTED FLUID PRESSURE COMPOUNDING SYSTEMS Steve Schnell,Kirkwood, Mm, assignor to Wagner Electric Our-notation, St. Louis, Mo.,a corporation of Delaware Application March 28, 1942, Serial No. 636,634

(Cl. Gib-54.5)

18 Claims.

My invention relates to fluid pressure actuating systems and moreparticularly to a system embodying improved means whereby a large volumeof fluid can be displaced during the initial increments of movement ofan actuated member and a smaller volume of fluid can be displaced duringlater increments of movement of said member.

One of the objects of my invention is to provide power-operated meansfor assisting in the displacement of the large volume of fluid in afluid pressure actuating system and thereby relieving the operator ofsome manual eifort.

Another object of my invention is to so construct said large volumefluid displacing means and associate therewith the power-operatedassisting means that said power means and the large volume fluiddisplacing means will automatically become inoperative when apredetermined fluid pressure is reached and subsequently assume theirnormally inoperative conditions without the necessity of a release ofthe fluid pressure below said predetermined value.

Other objects of my invention are to produce an eflicient low cost fluidpressure compounding system embodying means having a power-operatedmember for assisting in the displacement of a large volume of fluid andparticularly such means that it can be associated with the presentstandard parts of a fluid pressure actuating system.

Other objects of my invention will become apparent from the followingdescription taken in connection with the accompanying drawings in whichFigure 1 is a schematic view of a fluid pressure actuating systemembodying my invention; Figure 2 is a sectional view showing details ofthe power-operated means; and Figure 3 is a sectional view of thepressure-operated control valve means.

Referring to the drawings in detail and flrst to Figure 1, my improvedfluid pressure actuating system comprises, as essential parts, a mastercylinder device A, a power-operated device 13 for displacing a largevolume of fluid, and a pressure-operated control valve means C, saidsystem being shown as employed for actuating brakes D although otherdevices may be actuated if desired.

.The master cylinder A is of standard construction and comprises acylinder I having reciprocable therein a piston 2, said piston beingactuated by a piston rod 3 and pedal 4. Above the cylinder is areservoir 5 which is in free twoway communication with cylinder l bymeans of a compensating port a only when the piston is in its retractedposition where it is returned by a spring l.

A conduit 8. leads from the outlet of the master cylinder to branchconduits a and iii, the former leading to the power-operated device Band the latter leading to the pressure-operated control valve means C. Aconduit ii connects the power-operated device B with the fluid motors I2for actuatingthe brakes D. Another conduit 83 places thepressure-operated valve means C in communication with the fluid motors.

Referring to Figure 2, the power-operated fluid pressure displacingmeans'will now be described. This device comprises a casing member Mprovided with a large bore i5 and a smaller bore 16, bore it beingconnected to conduit 9 leading from the master cylinder and the largebore l5 being connected to conduit ll leading to the fluid motors of thebrakes. Within the large bore i5 is a piston ll to which is attached aforwardly extending hollow piston rod l8 havin bearing in a member i9threaded into the end of the large bore and acting as an end wallthereof. The piston ii is of annular constructionln order to provide abore 20 which is of the same diameter as the small bore I6, said bore 20forming a continuation of bore l6 when the piston is in its normallyinoperative position as shown in Figure 2. A packing cup 2i is carriedby the piston H for sealing it against passage of fluid when the pistonis moved forwardly,

said packing cup, however, not preventing fluid from flowing in theopposite direction. In bores i6 and 20 there is mounted a double-headedpiston 22, head 23 thereof being positioned in bore l6 and head 25 beingpositioned in bore 20. Sealing cups 25 and 26 are associated with heads23 and 24. The bore 20 communicates with bore l Sahead of piston IT byway of a passage 21.

The piston rod l8 for piston H is guided by a guide sleeve 28' integralwith member l9 and associated with the piston rod is a packing cup 29 toprevent any leakage of fluid from bore l5. The outer end of the pistonrod is connected to a piston 30 which is adapted to reciprocate in acylinder 3| mounted on member IS. 'The piston and cylinder form a vacuumfluid motor which is the power device employedfor actuating piston H. Aspring 32 acts on piston 30 and normally biases said piston to itsinoperative position, as shown in Figure 2, which inoperaitve p sitionwill correspond to'the inoperative posi- ,communicates with theatmosphere.

tion of piston I! as determined by its abutment with the end of largebore I5. The piston carries a sleeve 33 which surrounds the guide sleeve29 and a packing 34fis associated with the sleeves in order to make thecompartment 35 between the piston and member l9 fluid-tight.

The piston 30 carries a cup-shaped member 36 providing a valvecompartment 37, said compartment being in communication with compartment35 at the rear of piston 30 by an opening 38 through the wall of thepiston. The compartment also communicates with a compartment 39 ahead ofthe piston by way of a central opening 40 in the wall of member 36.Positioned within the valve compartment is a valve element 4| having asealing ring 42 for engaging the wall of member 36 which surroundsopening 40 to thus prevent communication between compartments 31- and39. One side of the valve member 4| carries an annular projection 43which slidably fits into the end of the hollow piston rod l8, said endbeing enlarged to receive a coil spring 44 for biasing the wave element4| toward a seated position. The other side of the valve element alsocarries an annular projection 45 and secured thereto is a tubularelement 46 which extends forwardly through the forward end wall ofcylinder 3|. Packing means 41 seals this tube with the end wall of thecylinder. The end of the projection 45 is provided with a sealing ring48 with which cooperates a valve element 49 formed as a head on the rod50 which extends completely through the hollow piston rod I8. Therear'end of this rod is secured to the double-headed piston 22. Packing5| seals the rod. The end of rod 50 adjacent the valve element 49 isfluted in order that air may flow along the rod and through a slot 52 inthe valve element 4| when the valve element 49 is unseated. It is thusseen that compartment 31 can be placed in communication with tube 46which Valve element 49 is normally held seated by a spring 53 interposedbetween the double-headed piston 22 and piston IT. This spring alsoholds element 4| unseated. against the bias of spring 43 when piston ITin the large bore and piston 36 are in their retracted positions. It isto be noted that when piston abuts the end of its bore, piston 22 isstill some distance from the end of bore l6 and, therefore, spring 53 isfree to expand and pull rod 50 rearwardly.

The end of cylinder 3| through which tube 46 extends has associatedtherewith an air cleaner 54 for cleaning the air before it passes intotube 46. The end wall of the cylinder also has attached thereto a tube55 which is connected to a suitable vacuum supply such as the manifold56 (see Figure l) of the engine of the vehicle. The compartment 39 incylinder 3| ahead of piston 30 is thus in constant communication withthis source of vacuum. When the valve element 4| is unseated,compartment 35 at the rear of piston 30 will also be in communicationwith the source of suction.

Referring now to Figure 3, the pressure-operated control valve means Cwill be described in detail. The valve means is enclosed within a casing57 provided with communicating bores 58 and 59, the former beingslightly larger than the latter. The end of the large bore is closed bya plug 66, which also serves as a connecting fitting for branch conduitl6 leading from the master cylinder. The end of the smaller bore isconnected with conduit l3 leading t9 $.11? fill-K motors of the brakes.The plug 60 has a central passage 6| and a cross-passage 62. A packingelement 63 is carried by the fitting between the cross-passage 62 andits inner end in order to prevent fluid from flowing from saidcross-passage to bore 59 and between the periphery of the fitting andthe wall of the bore. The packing cup, however, is so constructed as tocollapse and permit fluid under pressure to flow from the bore to thecross-passage 62.

Within bores-58 and 59 are pistons 64 and 65, respectively, formedintegrally with. each other. Piston 64 is provided with a projectingportion 66 which carries a valve element 61 for engage ment with thewall at the end of passage 6| of fitting 50. A spring 68 ofpredetermined strength is interposed between the small piston and theend of bore 59 in order to bias the valve element El seated and therebyclose passage 60. A passage 69 extends through the pistons so that whenthe valve element 67 is unseated, fluid can flow from conduit Hi toconduit 3 through the valve mechanism. Pistons 64 and 65 carry suitablesealing elements 10 and H. The pistons are capable of having only slightmovement in their bores, which movement is sufiicient to permit theunseating of the valve element 6'! against the predetermined forceexerted by spring 68. The amount of movement of the pistons isdetermined by the distance between piston 64 and the end of bore 58 whenthe valve element 61 is seated. I i 5 Since piston H in device B willmove forwardly and increase the volume of chamber 12 at the rearthereof, provision must be made to keep this chamber continuously filledwith liquid. This is accomplished by providing a conduit 13 forconnecting reservoir 5 of the master cylinder device "A with chamber 12.Associated with this conduit is a check valve 14 biased to closedposition by a spring 15. This check valve prevents fluid from flowingfrom chamber 12 to the reservoir but will not prevent flow in theopposite direction in order to keep the chamber filled. Inorder toassist flow of fluid from chamber 12 past piston l1 and packing cup 2|as the piston is retracted, holes 16 are provided in the wall of thepiston.

Referring now to the operation of the fluid pressure actuating system,all the parts thereof will be in the positions shown in the variousfigures when the system is inoperative. The valve element 61in thepressure-operated con trol valve means C will be closed by the action ofspring 68. Pistons I1, 22, and 36 will be in their rearmost positions asshown in Figure 2 and spring 53 will be effective to maintain the valveelement 49 seated and valve element 4| unseated. Under these conditionscompartments 39 and 35 on opposite sides of piston 30 will both be incommunication with the source of suction and due to this, there will beno force acting to move piston 36.

When it is desired to apply the brakes, the master cylinder A will'beoperated by actuating pedal 4. As soon as the compensating port 6 isclosed, pressure will be developed by piston 2 and this pressure will beefiective on piston head 25 of piston .22. No fluid can flow directlythrough the valve means C since passage 6| is closed. As soon assufficient pressure is developed to cause movement of piston 22 andcompress spring 53, rod 50 will be pushed forwardly. As this rod movesforwardly, spring 44 will be eifective to move valve element 4|therewith and cause seating thereof, thus closing off communicationbeassaoes tween compartments and .on opposite sides of piston 30.Continued movement 'of piston rod will now cause valve element 49 on theend thereof to be unseated, thereby permitting air under atmosphericpressure to enter the valve v compartment 31 and compartment 35 at therear of piston 30. This will now cause a dinerential fluid pressure toact on piston 30, therebymoving it to the left as viewed in Figure 2. As

the valve open will be that necessary to move piston 22 against thelight force of spring 53 and the fluid pressure which is being developedby piston l'l since head 24 of piston 22 is sub jected to the pressurein bore l5 due to opening 21 through piston i1.

The volume of fluid being moved by piston li, however, will be largerthan the volume of fluid being displaced by the master cylinder sincethe area of piston I1 is larger than the area of piston head 23 beingacted upon by the fluid pressure developed by the master cylinder. Ifpiston l'l should be twice as large as the heads of the double-headedpiston 22, the volume being displaced by piston It will be twice thatbeing displaced by the master cylinder. However, the pressure necessaryto obtain this displacement will only be that necessary to move piston22 against the action of spring 53 and the fluid pressure acting onpiston head 2d. The work necessary to move piston ill will be done bythe vacuum motor. If the head of piston H is twice as large in area asthe piston heads 23 and 26, as assumed, then the work necessary toaccomplish the displacement of a large volume of fluid by piston illwill be equally divided between the vacuum motor and the master cylindersince each causes the movement of a piston, the areas of which beingeflective' in acting on the fluid displaced are equal due to thearrangement including passage 21.

If the depressing movement oi the pedal should be discontinued, then thevacuum motor will also discontinue its operation. This is caused by thefollow-up type of valve means controlling the suction motor. As soon asrod 50 ceases to move, piston 36 will continue to move only enough toseat valve element d9, thus resulting in the pressures in compartments39 and 35 bearing such relation to each other that there will be adifferential force just sufilcient to hold pistons 36 and it against anyreturn movement by the fluid pressure already developed in bore it. Aspiston ii moves forwardly, fluid will constantly enter the expandingchamber iii from reservoir 5 and maintain it filled.

When the fluid pressure developed by the pistons i1 and it reaches apredetermined value it will cause valve elements? of valve means C to beunseated and maintained unseated against spring 53.

Xhe unseating .of the valve element 61? is brought about by the actionof fluid pressure on the larger area of piston 85, it being noted thatthis same pressure also acts on the small area of piston 8 due tothrough passage 69. When the force acting to move piston 5A to the leftbecomes greater than the force holding the valve 6? seated (spring forceplus force from fluid action on small area) the unseating will takeplace.

with valve element 61 unseated fluid will be capable of flowing directlyfrom the master cylinder to the fluid motors I! of the brakes. When thiscondition occurs, spring 53 can no longer be compressed since the pistonheads 22 and 24 at the opposite ends of piston 22 will both be incommunication with the master cylinder and, therefore, subject to thesame pressure. Spring 53 will now expand and the relative positions ofpistons I1 and 22 will be as shown'in Figure 2.

This will cause the valve element 49 to become seated and the valveelement 4| to become unseated. Both compartments 35 and 39 on'oppositesides of piston 30 will now be subject to the same sub-atmosphericpressure and there will be no force-tending to move piston 30 exceptthat of spring 32. This spring 32, which is fairly strong.

will now cause piston 30 to be moved rearwardly and will push piston I!also rearwardly. Piston i! will not be prevented from moving rearwardlyby the'fluid in compartment 12 at the rear thereof since this fluid canbe forced past the packing cupil by the action of spring 32 and into theportion of the bore ahead of the piston. Pistons I1 and 22 and thacuummotor piston 30 and the valve elements will finally assume the positionsshown in Figure 2 where they will be ready for subsequent operation. Thereturn of these pistons to their normally inoperative positions will nothave any effect whatsoever on the con-' cylinder through the valve meansC. Fluid under pressure can pass the valve element 67 notwithstandingthat it may be closed as return flow is permitted by the passage $3 thecollapse of the packing cup83 and the cross-passage d2.

If, during the retractile movement of the piston of the master cylinder,it is desiredto re-apply the brakes, the power-operated fluid pressuredisplacing means B will come into operation only when the fluid underpressure in the system is permitted to drop below the predeterminedvalue at-which the valve means C is opened. If the pressure is belowthis predetermined value, then the suction motor will becomeoperativeuntil the pressure exerted by the master cylinder piston isagain the predetermined value at which time the valve 61 will be opened.The vacuum motor will again become inoperativeand pistons l1 and 22automatically returned to their inoperative positions in the manneralready described.

It is thus seen from the described fluid pressure actuating system thatthere is provided means for displacing a large volume of fluid duringthe initial movement of the p ston of a master cylinder. The displacingof this large volume of fluid does not result in any additional efforton the operator since the vacuum motor does the work necessary to movethe extra volume as determined by the difierence between the areas ofthe pistons 22 and H. After the large body of fluid has been displaced,the master cylinder is automatically directly connected to the fluidmotors of the brakes and. the system acts as though the large volumedisplacing device were not incorporated in the system. All the parts ofsaid device automatically return to their normally inoperative positionsand without the necessity oi any release of fluid under pressure byrelease of the master cylinder piston. Because of the large volumedisplacing device being incorporated in the systom, the size of themaster cylinder piston may be reduced since it is not necessary for itto displace a large volume of fluid in order to get the brake shoesinitially applied and the slack taken up in the system. With a smallermaster cylinder piston, higher fluid pressures can be developed with thesame pedal ratio since a considerable amount of the pedal travel will besaved due to the fact that it is not required in displacing fluid totake up slack in the braking system. It is also to be noted that in theuse of the power-operated large volume fluid displacing device therewill be no noticeable eflect on the operator's foot at the time that thedisplacing device becomes inoperative and valve 6? is opened to directlyconnect the master cylinder with the fluid motors of the brakes. Whenthe power-operated device is being operated, the fluid pressure in thefluid motors of the brakes will be substantially the same (slightlylower) as that being develomd by the master cylinder. It is also to benoted in the system disclosed that there is no necessity for a speciallydesigned master cylinder as the poweroperated large volume displacingdevice B and the valve means 6' may be interposed in the fluid pressurelines wherever it is convenient. Of course, the device B and valve C maybe specially designed into the master cylinder to make a single unit ifsuch is desired. It is very easy to install the units in any existingbraking system and the cost thereof will be low since it will not benecessary to replace the master cylinder already being employed in thebraking system.

Being aware of the possibility of modifications in the particularstructure herein described without departing from the fundamentalprinciples of my invention, I do not intend that its scope be limitedexcept as set forth by the appended claims.

Having fully described my invention, what I claim as new and desire tosecure by Letters Patent of the United States is:

1. In a fluid pressure actuating system, a fluid motor for actuating adevice, a master cylinder device connected to the fluid motor, apoweractuated fluid pressure displacing device connected to the fluidmotor and having a source of power independent of the master cylinderdevice, means for preventing the fluid under pressure developed by themaster cylinder from being transferred to the motor until apredetermined fluid pressure is attained in the fluid motor, and meansfor controlling the operation of the poweractuated device by fluidpressure from the master cylinder prior to said master cylinder beingconnected to the motor.

2. In a fluid pressure actuating system, a fluid motor for actuating adevice, a master cylinder device connected to the fluid motor, means forpreventing the fluid pressure developed by the master cylinder frombeingtransferred to the motor until after a predetermined pressure isreached, means comprising a power-actuated fluid displacing devicehaving a source of power independent of the master cylinder device andcontrolled by the fluid pressure developed by the master cylinder priorto said predetermined pressure for placing fluid under pressure in thefluid motor, and meansfor causing the power-actuated fluid pressuredisplacing device to become inoperative whenever the pressure developedby the master cylinder device is above the predetermined pressure.

3. In a fluid pressure actuating system, a fluid motor for actuating adevice, a master cylinder device, conduit means for placing the mastercylinder device in communication with the fluid motor, valve meansassociated with the conduit for preventing said communication until apredetermined pressure is developed by the master cylinder device, afluid displacing device connected to communicate with the motor andincluding a movable member, power means independent of the mastercylinder device for operating the movable member, and means controlledby the fluid,

pressure developed by the master cylinder when said pressure is belowthe predetermined value l for causing said power device to be operable.

4. In a fluid pressure actuating system, a fluid motor for actuating adevice, a master cylinder device, conduit means for placing the mastercylinder device in communication with the fluid motor, valve meansassociated with the conduit for preventing said communication until apredetermined pressure is developed in the fluid motor, a fluiddisplacing device connected to communicate with the motor and includinga movable member, a second fluid displacing device also connected withthe motor and including a movable member, power means having a source ofpower independent of the master cylinder device for operating themovable member of the first fluid displacing device, and meanscontrolled by the fluid pressure developed by the master cylinder whensaid pressure is below the predetermined value for causing said powerdevice to be operable and also the movable member of the second fluiddisplacing device to be moved to displace fluid.

5. In a fluid pressure actuating system, a fluid motor for actuating adevice, a cylinder connected to communicate with the motor, a piston insaid cylinder. a source of power and power-operated means for actuatingthe piston, control means for the power means, a source of fluidpressure, means for operating the control means by pressure from thesource, and means for placing the source in direct communication withthe motor when the pressure in the motor reaches a predetermined valueto thereby operate the fluid motor independently of the power means andits source of power.

6. In a fluid pressure actuating system, a fluid motor for actuating adevice, a cylinder connected to communicate with the motor, a piston insaid cylinder, a source of power and poweroperated means for actuatingthe piston, control means for the power means, a source of fluidpressure, means for operating the control means by pressure from thesource, means for placing the source in direct communication with themotor when the fluid pressure in the motor reaches a predetermined valueto thereby operate the fluid motor independently of the power means andits source of power, and means for causing said power means to beinoperative and the piston to return to its normally inoperativeposition after said direct communication is established.

7. In a fluid pressure actuating system, a fluid motor for actuating a.device, means comprising two movable members for developing fluidpressure to actuate the motor, a source of power and power operatedmeans for actuating one of the members, means for controlling theoperation of tially simultaneous movement, a source of fluid pressure,means for moving said other member by pressure from the source, andmeans for placing the source in direct communication with the fluidmotor when a predetermined fluid pressure is eiiectivein the fluid motorto thereby operate, the motor independently of the power means and itssource. I

8. In a fluid pressure actuating system, a fluid motor for actuating adevice, means comprising two movable pistons for developing fluidpressure to actuate the motor, a source of power and power operatedmeans for actuating one of the pistons, means for controlling the powermeans by the movement of the other piston so that said pistons will havesubstantially simultaneous movement, a source of fluid pressureindependently of the source of power for the power means, means formoving said other piston by pressure from the source, and comprising afluid motor connected to the source and having a piston the samediameter as said other piston, and means for placing the source indirect communication with the fluid motor when a predetermined fluidpressure is efiective in the fluid motor. 9. In a. fluid pressureactuating system, a fluid motor for actuating a device, means comprisingtwo movable membersfor developing fluid-pressure to actuatethe motor,power means for actuating one of the members, means for controlling thepower means by the movement of the other member so that said memberswill have substantially simultaneous movement, a master cylinder device,means for. moving said other member by pressure developed by the mastercylinder device, means for placing the master cylinder device in directcommunication with the fluid motor only when the pressure beingdeveloped by the master cylinder device is above a predetermined value,and means for causing the power means to be inoperative when thepressure developed by the master cylinder device is abovethepredetermined value.

10. In a fluid pressure actuating system, a fluid motor for actuating adevice, a fluid pressure developing chamber connected to the motor, twomovable members acting on the fluid in the chamber, power means formoving one member, control means for the power means, means forcontrolling the control means by the movement of the other movablemember so that the power means moves the first movable membersubstantially simultaneously with said other movablemember, a source offluid pressure independently of the source of power for the power means,means for moving said other movable member by pressure from the source,means for connecting the source to the motor when the pressure from thesource is above a predetermined value, and means for preventing thepower means from functioning when the source is connected to the motor.

11. In a fluid pressure actuating system, a fluid motor for actuating adevice, a fluid pressure developing chamber connected to the motor, twomovable members acting on the fluid in the chamber, a suction motor formoving one member, a follow-up valve mechanism for controlling thesuction motor, means for controlling the valve mechanism by the movementof the other movable member so that the suction motor moves the firstmovable member substantially simultaneously with said other movablemember, a

source of fluid pressure, means for moving said other movable member bypressure from the source, and means for connecting the source to themotor when the pressure from the source is above a predetermined value.

12. In a fluid pressure actuating system, a fluid motor for actuating adevice, a fluid pressure developing chamber connected to the motor, twomovable members acting on the fluid in the chamber, a suction motor formoving one member, a follow-up valv mechanism for controlling thesuction motor, means for controlling the valve mechanism by the movementof the other movable member so that the suction motor moves 13. In afluid pressure actuating system, a

fluid motor for actuating a device, a chamber connected to the fluidmotor, first and second pistons for placing fluid in the chamber underpressure, a suction motor for moving the first piston, a follow-up valvemechanism for control-, ling the suction motor, means for controllingthe valve mechanism by movement of the second piston, a master cylinderdevice, means for moving the second piston and comprising a. thirdpiston subject to the fluid pressuredeveloped by the master cylinderdevice, said second and third pistons being of equal diameters, andmeans for placing the master cylinder device in communication, with themotor when the pressure developed thereby is a predetermined value.

14. In a fluid pressure actuating system, a fluid motor for actuating adevice, a cylinder in communication with said motor, a piston movableinsaid cylinder for displacing fluid under pressure to the fluid motor,means comprising a second piston for acting on the fluid in saidcylinder, power means for moving the first piston, control means for thepower means, a master cylinder device, means for moving the secondpiston by fluid pressure developed by the master cylinder device, meansfor controlling the control means of the power means by the movement ofthe second piston so that the power means moves the first pistonsubstantially simultaneously with the second piston, means for directlyplacing the master cylinder device in communication with the motor whenthe pressure in the fluid motor is greater than a predetermined value, areservoir, means for establishing a chamber at the rear of the firstpiston,- means for connecting the reservoir to the chamber soas tomaintain said chamber filled as the piston moves forwardly, and

means for preventing fluid from said cylinder to Y return to thereservoir.

15. In a fluid pressure actuating system, a fluid motor for actuating adevice, a cylinder in commumcation with said motor, a piston movable insaid cylinder for displacing fluid under pressure to the fluid motor,means comprising a second piston for actuating on the fluid in saidcylinder, power means for moving the first piston, control means for thepower means, a master cylinder device, means for moving the secondpiston by fluid pressure developed by the master cylinder device, meansfor controlling the control means of the power means by the movement 01.the second'piston so that the power means moves the first pistonsubstantially simultaneously with the second piston, means for directlyplacing the motor, a piston in said cylinder for displacing fluid .andprovided with a bore in communication with the cylinder, a second pistonin the bore, a

fluid motor connected to move the first piston, a

master cylinder device in communication with the motor when the pressurein the fluid motor is greater than 'a predetermined value, a reservoir,means for establishing a chamber at the rear of the first piston, meansfor connecting the reservoir to the chamber so as to maintain saidchamber filled as the piston moves forwardly, means for preventing fluidfrom said cylinder to returnto the reservoir, means for permitting fluidto flow fromthe chamber tothe cylinder ahead of the piston but not inthe opposite direction, and spring means for returningthe first pistonto its normally inoperative position when the master cylinder is indirect communication with the motor.

16. In a fluid pressure actuating system, a fluid motor for actuating adevice, a master cylinder device, conduit means for placing the mastercylinder device in communication with the fluid motor, valve meansassociated with the conduit for preventing said communication until apredetermined pressure is developed by the master cylinder device, acylinder connected with the motor, a piston in said cylinder fordisplacing fluid and provided with a bore in communication with thecylinder, a second piston in the bore, a fluid motor connected to movethe first piston, a follow-up valve mechanism for controlling theoperation of the last named fluid motor, means for operating thefollow-up valve mechanism in accordance with the movement of the secondpiston, and means for moving the second piston by the fluid pressuredeveloped by the master cylinder when said pressure is below thepredetermined value.

17. In a fluid pressure actuating system, a fluid motor for actuating adevice, a master cylinder device, conduit means for placing the mastercylinder device incommunication with the fluid motor, valve meansassociated with the conduit for preventing said communication until apredetermined pressure is developed by the master cylinder device, acylinder connected with the follow-up valve mechanism for controllingthe operation oi the latest named fluid motor, means for operating theaccordance with the movement of the second piston, means for moving thesecond piston by the fluid pressure developed by the master cylinderwhen said pressure is below thepredetermined value, means forestablishing a chamber at the rear of the first piston, a reservoirconnected ,to said chamber, a check valve between the reservoir andchamber, means for permitting fluid to flow from the chamber past thefirst piston to the cylinder ahead thereof but not in the oppositedirection, and a spring acting on the first piston tending to return itto its normally retracted position.

18. In a fluid pressure actuating system, a fluid motor for actuating adevice, a master cylinder device, conduit means for placing the mastercylinder device in'communicationwith the fluid motor, valve meansassociated with the conduit for preventing said communication until apredetermined pressure is developed by the master cylinder device, acylinder connected withthe motor, a piston in said cylinder fordisplacing fluid and provided with a bore in communication with thecylinder, a second piston in the bore, a fluid motor connected to movethe first piston a follow-up valve mechanism for controlling theoperation of the last named fluid controlling the operation of the lastnamed fluid motor, means for so controlling the follow-up valvemechanism by the movement of the second piston that the first pistonwill be moved by the fluid motor substantially simultaneously with.

said second piston, and means for moving the second piston by the fluidpressure developed by the master cylinder when said pressure is belowthe predetermined value, said last named means comprising a fluid motorconnected to the master cylinder and having a piston the diameter ofwhich is the same as the diameter of the second piston.

STEVE SCHNELL.

follow-up valve mechanism in

